Sensorineural deafness is by far the most common type of hearing loss. Deafness affects 9 million people in the United Kingdom, of which about 95% have sensorineural deafness (source Defeating Deafness, United Kingdom). Causes include congenital, bacterial, high intensity noise and, especially, the ageing process, with 30 percent of those affected being over 60 years. Hearing impairment is the third most common chronic problem affecting the ageing population—and one of the least diagnosed. There is also an increased prevalence in some sections of the younger age group, due to exposure to loud noise.
There are currently no effective means of repairing the cochlea or the nervous pathways to the brain. For most patients, hearing can be restored adequately by sufficient amplification of sound with a hearing aid. Hearing aids have a number of problems: acoustic feedback (because the microphone is very close to the speaker), inadequate sound quality, and discomfort due to occlusion of the ear canal. They also are undesirable from the social point of view, in that the appearance of wearing a hearing aid can cause users to feel that they are seen to be handicapped. The alternative is an implantable device.
Middle ear implants provide mechanical amplification by vibrating the ossicular chain. They are intended for patients with moderate to severe sensorineural hearing loss, who still have residual hearing. They could potentially benefit up to 50% of all people with hearing loss. Cochlear implants, the alternative, provide electrical stimulation to the nerves of the inner ear, but are suitable only for the profoundly deaf, as all residual hearing is destroyed during their implantation. They are not favoured where there are alternative solutions.
Middle or inner ear implants however require a power supply. A few use incorporated batteries, which although last several years, require replacement. This undesirably necessitates a further operation for the patient. Other implants use wires through the skull and the rest use radiofrequency or inductively coupled methods. Nevertheless, radio frequency modulated transmission uses complicated circuitry, is cumbersome and costly, and the implanted receiver module itself has a heavy demand on power. It also has to be approved under each country's radiofrequency regulations. Inductively coupled transmission methods use two coils or one coil and one magnet separated in close proximity. However, problems include high power consumption, signal variations and background noise. Moreover, MRI compatibility can also be a problem with some components.
It is an object of the present invention to obviate and/or mitigate at least one of the aforementioned disadvantages and/or problems.